This invention relates to a thermosensitive recording medium having a support and a thermosensitive color-developing layer formed on the support and containing a leuco dye and a color developer capable of reacting with the leuco dye at an elevated temperature to develop a color.
Thermosensitive recording media capable of thermally recording an image through coloring reaction of a colorless or light-color leuco dye with a developer such as a phenol compound are now increasingly utilized in various fields such as recording papers for printers of computers, medical measuring instruments and facsimile machines, automatic ticket vending machines, thermosensitive copying machines and POS (point of sales) labels.
One problem of the known thermosensitive recording media is that the images and background are apt to be discolored when the thermosensitive layer thereof is brought into contact with a plastic film containing a plasticizer. To cope with this problem, a protecting layer is generally provided to cover the thermosensitive layer. The protecting layer is also desired to have lubricity or slippage in order to ensure smooth sliding between the recording medium and a thermal head, i.e. smooth feeding. When the thermosensitive recording medium is not smoothly fed, the recorded images are shrunk in the feeding direction. Thus, there is a proposal to incorporate a wax such as zinc stearate or montan wax into the protecting layer. While zinc stearate shows good lubricity, the resistance to plasticizers is not satisfactory. Montan wax, on the other hand, has good resistance to plasticizers but is not fully satisfactory with respect to lubricity.